Doppler radar system



Filed may 50, 1945 2 SHEETSSHEET 1 FIG.

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DEFT H, DC/E By /V'MWMQ MM Sek, @952 R. H. DlcKE NZS DOPPLERRADAR SYSTEM Sept. 16, 1952V R, H, DICKE DOPPLER RADAR SYSTEM Filed May 50, 1945 2 SHEETS--SHEET 2 FIG 3 ea) @INK TI R F SOURCE 63 DUPLEXING MEANS 6s v 14 L64 we LMIXEI |F DELAY AMP NETWORK 95 |o|` |o2- g3 -C/lV/Ty n 06g MIXER MXER VLS i1 3 92A' sa o L P 'C5 L p Ds @l FILTER HUE@ To A To B Iox AF AMP f IND.

Ilvl/ENTOPh ROBERT :Mmm-2 Patentedv Sept. 16, 1952 A DOPPLER RADAR SYSTEM Robert H. Dicke, Cambridge, Mass., assigner, by mesne assignments, to'the United States of America as represented by the Secretary of War Application May 30, 1945, Serial N0. 596,726

Claims. 1

This invention'relates to communication systems and more particularly toV such systems as used for determining the relative velocities of two or more objects.

According to the theory of the Doppler effect, if a wave of energy of a given frequency emanates 'from one object and strikes another object, the 'observed frequency of the energy at the second object, or as observed when reflected back to the first object, will be different from the given fre,- `quency if the two objects are moving relative to each other. The change in frequency is propor- "htional to the relative velocity of the two objects. "This effect hasbeen used to determine the velocities of objects such as projectiles and airplanes andto detect the presence of moving objects, Qmen, vehicles, airplanes, etc. The complications inherent in such a system have limited their use heretofore to low power transmitters and relatively low gain receivers. I f An object of the present invention is, therefore, to provide an'improved system for detection o moving objects.

Another object `o f the present invention is to provide, in a system for detection of moving ob` jects, a device for suppressing the center IF frequency to prevent overloading of the intermediate-frequency amplifier.

Another object of the present invention is to provide a system for detection of moving objects inwhich noise and other extraneoussignals are minimized. Y

In accordance with the present invention a first 'oscillator is connected to a transmitting means and to a single sideband modulator. A receiving means is connected to a rst mixer. A second oscillator, operating at the intermediate frequency, is connected to the single sideband modulator and to a second mixer. Thefsingle sideband modulator Vconnects to the iirst mixer. ',The output of the first mixer connects to an intermediate-frequency amplifier which in turn feeds the lsecond mixer. The second mixer feeds Van indicater; For a better understanding of the invention, together with other and-further` objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawings in which: I Fig. 1 is a diagram schematically showing an embodiment o'f the invention with separate transmitting and receiving antennae; `Fig. 2 is a diagram of an embodiment of the invention using a duplexing device and a single antenna for transmitting and receiving; and

Fig. 3 is a diagram of an embodiment of the invention using a duplexing device,` single antenna, and an automatic `impedance matching device for reducing undesired signals. Y

Referring now more particularly to Fig. 1 of the drawings, there is shown a Doppler type velocity detecting system having separate transmit:- tins. any1 ,receiving antennae A sevres. 'l of conf l(c1. 34a-s) tinuous wave (CW) radio frequency energy is 'connected to an antenna I2. The source II also feeds a single sideband modulator I3, preferably by use of a directional coupler, not shown. A

4local oscillator source I4 of lintermediate-frequency (IF) energy also connects to the modulator I3. The modulatorI3 may be a conventional mixer circuit with provision for eliminating the undesired sideband or it may be, asis preferable, a single sideband modulator such"as is disclosed and claimed in the ccpending `application of Robert H. Dicke, Serial No. 595,359, led May 23, 1945, now Patent No. 2,496,521. A load I5 is connected to the modulator I3.-` The modulator I3 is also connectedto a mixer I6, An antenna 2| also connects to the mixerg'l.

The mixer I6 connects to an IF amplifier 22 which in turn connects to a second mixer 23. The mixer 23 is connected to the source I4 and to an indi'- cator 24. The mixers I6 and 23 may be any conventional type `of frequency mixer, crystal, v acuum tube or other device. The indicatorZfI' may be any suitablelindicator, preferably givingan indication proportional to input frequency. p The preferred type is a frequency or spectrum analyzer such as disclosed and claimed in thecopending application of Robert H. Dicke, Serial No.` 581,696, filed March 8, 1945, now Patent No. 2,527,712. The preferences herein stated are not to be taken as limitations of the invention.

In the operation of the system of Fig. 1, the source II sends energy to the antenna I2 where it is radiated in a directional beam. When this radiated energystrikes an object, some energy is reflected. If the object is moving relative to the antennae I2 and 2l, the energy returned to and received by the antenna ZI will differV in' frequency from the transmitted energy. The received energy passes on to the mixer I6. A portion of the energy from the source I I is combined in the modulator I3 with energy from the local oscillator I4. The modulator I3 produces an upper sideband of energy whose frequency is the sum of theltwo input frequencies, and a lower sideband of energy whose frequency is thediffer.- ence of the two input frequencies. The load'I5 is provided to absorb the undesired sideband. The remaining sideband is fed to the mixer I6 where it is mixed with the received energy. The energy received by the antenna 2l directly from the antenna I2 and from stationary objects combines with the energy from modulator I3 to produce a signal at the intermediate frequency. Energy received by the antenna 2!` from moving objects combines with the energy from the modu: lator I3 to produce a signal having a, frequency differing from the 1F by the same amount the received signal frequency differs from the trans-A mitted signal frequency. The output of the mixer I6 is fed to the amplifier 22 Where it is amplified and fed to the mixer 23. In the mixer 23 these signals are combined with IF from source I4, which Ahas aconnection 25 to the mixer. i In some '1 tffthejdrawingsl..waargenomi agmitodment of the invention with provisions for maintaining the signal received from stationary objects at is effective, in accordancef.-with its: frequcrlm- 15,012

produce an indication proportional;toithefvelocity of the object observed.

Referring now more particularly tdFig. 2. of i the drawings, there is shown another embodiment of the invention which utilizesronl'yaone, antenna and a duplexing device. A source 3|, .similar to source I of Fig. 1, connects to a branch 3,2/ofl1l.duplexingv device L33. A .load 34 terminates. albranch 35` ofthe device33 and-.an antenna'Sconnects'tofa branch4l of the device Yf A branch 42 of 4'the device'33 connects to a.lmim'arlti..l The .duplexing device .may beany onelof. several such devices well knownin'` the art VTuning devices 44 permit adjustment of the ,dei/icel33.v local oscillator 45similar vto local oscillator |4. of Figi, oonnectsto a modulator '46. vsimilar to modulator, I3 of Fig. r1. rThe modulator.4Ev is. connected to thesource 3|, to the mixer43'andto ay load 41., The mixer 4'3 connects'to anIFamplifierSi which in ,turn connects tofa mixer .52 whichis similarto the mixer23. of Fig'. l. .The mixer 52 is, connected to thetlocal Ioscillator 45. and toan audio ampli- `iie 1'f'."13. .The .amplifie`r153 feeds an indicator 54 which is similarL tothe indicator, 24 ofv Fig. 1. -.'Ihe..operation.of this's'ystem is'the lsame in ugeneral{as}the.,systemof Fig 1. lEnergy from .the,s o 1rce1`3| passes into the duplexing device -33."..This energy 'divides as show-n by the solid arret/s55. Part of the energy is absorbed by the' loadj. 341and 1the remainder. passesA on ,to .the antennaSS Av'vhere'it'is radiated, 'The tuners 4.4,.are adjustedfso. that none of this transmitted energy. passes to 4the mixer 43. The received energy from antenna 3S divides -as vinsiicated bythedashedarrows 58. Part of the energy passes back i'nto. the source 3| where it Will be absorbed and the remainder passes intof the ,'rnixer 43. It can be, shown that if the antenna 3,6' is" twice, the size of the antenna 2 or 2I the same energy Will be transmitted to and received from any Vgiven object despite Vthefact that both in .transmission and, reception one-half ofthe energy is lost. @In the mixer43received lenergy u isjcombined with energyfrom the modulator 4B asfdescribe'd in detail'for Fig. 1. The out 'putofthe mixer 4 3 isJfed to VtheIl',amplifier 5 If. As was stated in the'discussion of the system of Fie. 1, reiiections from stationary objects will produce energy4 at the intermediate frequency in the output ofimixer 43. vThis energy maybe troublesome' if present in suflicient quantity to causean amplifier to be saturated oroverdriven. Therefore, itis desirable that the .amplifier 5| have W gain to prevent this saturation. The ouputoi the amplifier 5| feeds'the mixer'52 Where it is combined with energy from the local oscillator 45 to produce DK. C. and audio signals.

The mixer 52 drivesy the high gain' audio amplier. If IFv amplifiersi are lovvg'gain, it is necessaryto have the high gain audio amplifier 5 3' to raise the 'signalstopa 4sufiiciently high level toffoperateA the indicator 54.. Atv the indicator 54the frequency ofthe audio signals determines the indicatedvelocity of observed objects. v'This embodiment 'is notlimited rto' the low grain IF and ,a. minimum. This system comprises a source *6|,"simi1ar"to the source of Fig. 1, connected '5.O ';a-branch;j62 of `a duplexingr device 63. The

::dnplexing-cdevce -563 is similar to the device ,'33xof1-Fig. :A'terminal 64 of the device 63 high gain audio amplifier as shownbut may be used as in'Fig. lwith the addition ofthe duplexin'g device 33.` Referring "now mmore particularly tol Fig; 3

.connects to an antenna E5 or other radiatingreceivingdevice. A terminal 6e of the device 63 .connects to a mixer 1| which is similar to the mixer I6 of Fig. 1. A-terminal 12 of the device 63. connects-to a. load 73. The loadl3. consists of A aT11-.bridge vor magie-'Tfl which,.,may.be

f ,similar .in construction to .the ,device563f Abut fitted with loads, preferably silicon,crystalfs,.15 and 'i3 located in the symmetricalbranches of .them,aggi'c-',` at Aelectrical Vdistances D1.. alfd Dit from.. the;center.of themagiclT 1,4'. The distanceDiexceeds' the distance D2 by an oddnum- .ber of eighthA wavelengths. Input terminalsto the loads Hiand 'i6 arelabeledA and. B. ;A load ,8l .terminates the remaining branch of Athe magi'l` 14...V The source, 6| is also vconnected througha .directional couplerEZ to a 'singlesidebandmodulator. The modulatorS comprises two mixers. 8,4 andlB insertedinthe sym,- metrical branches B6 .andl of a magici-TL92 at d istances`.. Darand D4 fromthe .center vofthe magic-.T"92. The distances Dis and D1 differb'v one-.eighth wavelength. The mixers 84and.,85 are separated at the intermediate, frequencyby aouarter wave delayfline4 9 3,.the. mixer 8 4 being connected .to a local oscillator sourcetof IF energy. The circuit represented in.block .83 .i s .disclosed andY claimed in the above ,mentioned copending .application of.. Robert. I-I. Dicke.. Serial N. 595,359, ld. May 23, 19.45. lT'Ifhe'.outp'iAtLof themodulator 83 connects'tothe .mixer 1|. .In some cases it may be desirableto,make',this.con nection through, as elective cavity The selec- .tive.cavityfformsa load circuit which is high- `ly selective in the frequency of energy Whichit allows to pass through it. It might becalled a very. narrow, bandfpass lter. The mixenl connects to. an IF amplier; St which connects ,toamixerl |0| directly and to .amixer m2 through a quarter Wave delay. linei |l|3. The mixersl lil] and |!2 areconnected,tothesourceefl and .tolow pass filters- |U 4 and' |315. The outputs of Jfthe iiltersl |04 and. il! 5. are labeled toQAfand to'Bf and connect. .to .'.terminals A and. B. respectively of. the. load 13. In addition, the mixer 10| conf nectsto an. audio amplifier we. which vfeedsxan indicatorH |01. .The indicator ..||i`| is.,similar-.to the indicator 24 of Fig. 1. AThis inventiongis not -limitedto the use of the-type .of singlesidebandmodulatorsshovvn..- y

lTheo-poration of. the vsystem of. Fig.l 3V` ,sim-.- ilarf tof 'theoperationofthefsystemwof. Eig. Only those'parts which differ will be discussed. The; mixer- 1 `may bea balancedimixer vor af conventional single elementmixer. If f a1 balanced mixer is used, the usei'off' thecavity loadacircuit 95 yis recommended. Stationary objects, and' especially nearbyl objects, .cause thezan'tenn'a im# pedancetovary.; as: searching' is: accomplished.- This variation of antenna impedancefresultsdn unbalance-:at'ithe1duplexer'-63. The undesirabley intermediatefrequency -'energy produced in fthe mixer |02 in conjunction with the filters |04 and |u5 mak-e it possible to maintain the load 'I3 automatically matched to the antenna 65 and thus minimize the undesired IF energy. In the design ofthe apparatus it is necessary that the proper phase relationships be attained to provide inverse feedback from the filters |04 and |85 to the load 13, through the mixer IF amplifier 96 and back to filters |94 and |65.

While all three embodiments herein shown and described have been treated from the standpoint of a Doppler type system employing continuous wave transmission, the device will operate equally well if frequency modulation is used. No changes in the electrical circuits are necessary other than changing of the type of radio frequency source used.

While there have been -described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention.

I claim: v

l. A communication system for determining the relative velocity of two or more objects comprising duplexing means, a transmitting oscillator connected to said duplexing means, radiating means connected Ito said duplexing means, variable loading means connected to said duplexing means and having first and second input means, a local oscillator, fa single sideband modulator connected to said transmitting oscillator and said local oscillator, a first mixer connected to said duplexing means and to said modulator, a first amplifier connected to the output of said first mixer, a second mixer connected to the output of said first amplifier and to said local oscillator, first filter means connecting a portion of the output of said second mixer to said first input means of said loading means; a second amplifier connected to a portion of the output of said second mixer, an indicator adapted to utilize the output of said second amplifier, de-

lay means connected to the output of said first amplifier, a third mixer connected to the outputs of said delay means and said localoscillator,

and second filter means connecting the output of said third mixer to said second input means of said loading means, whereby said indicator indicates the velocity of a reflecting object relative to said radiating means.

2. A communication system for determining the relative velocity of two or more objects comprising dupiexing means, transmitting oscillator means connected to said duplexing means, radiating means connected to said duplexing means, local oscillator means, single sideband modulator means connected to said transmitting oscillator means and to said local oscillator means, loading means connected to said modulator means, rst mixer means connected to said duplexing means and said modulator means, second mixer means, first amplifier means connecting said first mixer means to said second mixer means, said second mixer means being also connected to said local oscillator means, indicator means, and second amplifier means connecting said second mixer means to said indicator means, said indicator means being adapted to utilize the output of said second amplifier means to indicate velocity of a reflecting object relative to said radiating means.

3. A communication system for determining the relative velocity of two or more objects comprising transmitting oscillator means, means for radiating and receiving connected to .said oscillator means, local oscillator means, single sideband modulator means connected to said transmitting oscillator means and to said local oscillator means; means for absorbing the unwanted output frequencies of said :modulator means coupled to said modulator means, first mixer means connected to said means for radiating and receiving and said modulator m-eans, second mixer means coupled to said local oscillator means, amplifier means coupling said first mixer means to said second mixer means', and indicator means adapted to utilize the output of said second mixer means.

4. A communication system for determining the relative velocity of two or more objects comprising duplexing means, first oscillator means connected to said duplexing means, radiating means connected to said duplexing means, variable loading means connected to said duplexing means and having first and second input means, second oscillator means, modulator means connected to said rst and second oscillator means, first mixer means connected to said duplexing means, frequency selector means connected between said modulator means and said first mixer means, first amplifier means connected to the output of said first mixer means, second mixer means connected 'to the output of said rst amplier means `and to said second oscillator means, first filter means connecting a portion of the output of said second mixer means to said first input means of said loading means, delay means connected to `the output of said rst amplifier means, third mixer means connected to the output of said delay means and said second oscillator means, second filter means connecting the output of said third mixer means to said second input means of said loading means, second amplier means connected to a portion of the output of one of said second and third mixer means, and indicator means adapted to utilize the output of said second amplifier means.

5. A communication system for determining the relative velocity of two or more objects comprising duplexing means, transmitting oscillator means connected to said duplexing means, radiating means connected to said duplexing means, local oscillator means; single sideband modulator means connected to said transmitting oscillator means and to said local oscillator means, loading means connected to said modulator means, first mixer means connected to said duplexng means and said modulator means, second mixer means coupled Ito said local oscillator means, amplifier means coupling said first mixer means to said second mixer means, and indicator means adapted to utilize the output of said second mixer means.

ROBERT H DICKE REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,134,716 Gunn Nov. 1, 1938 2,435,569 Barrow Feb. 10, 1948 2,479,568 Hansen Aug. 23, 1949 FOREIGN PATENTS Number Country Date 472,891 Great Britain Sept. 29, 1937 

